1. Field of the Invention
This invention relates to means for amplifying an optical signal, and, in particular, to a device comprising a high gain compound semiconductor heterojunction bipolar transistor operated in a common emitter configuration coupled to a light-emitting device in a monolithic structure.
2. Description of the Prior Art
At present, low level signals are typically preamplified by several stages of silicon transistors and then used to drive a light-emitting diode (LED) or diode laser for launching optical radiation into a fiber optic waveguide. Silicon current amplifiers are disclosed in, e.g., U.S. Pat. No. 2,569,347.
A bipolar heterojunction phototransister capable of current gains of up to 1600 has been disclosed in Vol. 48(10), Journal of Applied Physics, pp. 4389-4394 (1977). The device comprises undoped n-type GaAs (collector), p-type GaAs (base) and n-type Ga.sub.1-x Al.sub.x As (emitter), operated in common emitter fashion.
Monolithic integration of GaAs/GaAlAs bipolar transistor and heterostructure laser is disclosed in Vol. 37(2), Applied Physics Letters, pp. 211-213 (1980). Current gains of up to 900 are realized.